x8

DYEING AND CALICO PRINTING.

the air, but when mingled intimately with nitrogenised and especiallyalbuminous substances, as in wood, the case is different. These substancesare very prone to decompose, and when once their molecules are set inmotion that motion is gradually imparted to the entire strudture. The resultis a slow combustion, which, assisted by air and moisture, soon destroys thesubstance, converting it by a series of metamorphoses, and by a processcalled by Liebig ercmacausis , into a variety of organic compounds, includinghumin, ulmin, and humic and ulmic acids. According to M. Pasteur, the rottingof wood is due to the presence of infusoria which feed upon the albuminoussubstance contained in it; but as this theory has been the subjedt of muchcontroversy we will not enter upon it here. Very dilute acids exercise nomarked adtion upon cellulose even at boiling heat, but the adtion of con-centrated acids is entirely different and very important from a practical pointof view.

When pure cellulose, cotton for instance, after being thoroughly bleached,is placed in concentrated phosphoric or sulphuric acid at the ordinarytemperature, it becomes disintegrated, and dissolves, colouring the acid. Itchanges into a viscous mass consisting of dextrine, which has the samechemical composition as cellulose ; the only real change is, therefore, amolecular change. If the acid solution is largely diluted with water and thenboiled, the dextrine fixes the elements of the water and is converted intoglucose. If cellulose be treated with moderately diluted nitric, sulphuric, orhydrochloric acids and subjedt to the adtion of heat, disintegration occurs, andthe result is a somewhat thickish mass apparently insoluble in water, andsimilar in its composition to cellulose. According to Dr. Calvert, ofManchester, an adtion almost as destrudtive as that of dilute mineral acids isexercised upon cotton and linen fibre by several organic acids. This statementled to some enquiries on the subjedt by M. A. Dollfus. The acids used wereoxalic, tartaric, and citric, these being most often employed in printing calico,muslin, and other tissues. Pieces of very fine linen tissue and of muslin, afterbeing thoroughly washed in distilled water, were steeped in aqueous solutions,each containing 2 per cent of vegetable acids. They were then dried in air,and exposed for one hour to respedtive temperatures of 176°, 212 0 , and 258’8°,with the results shown in Table I., p. 19.

Oxalic acid exerts a destrudtive influence equal to that of mineral acids.Among the pieces of tissue soaked in the acids aboved named, that which wassteeped in oxalic acid assumed the darkest shade of brown, proving that thealteration is in diredt proportion to the colouration.* Dr. Calvert’s experimentsmade with solutions containing 4 per cent of water led to the results shownin Table II., p. 19. According to this author aqueous solutions of theseacids containing 2 or 4 per cent adt better when gum or gelatine is added tothem in the proportion used for thickening, and the tissues exposed to thesame temperature. The researches of M. Dollfus tend to prove the reverse,for in his experiments solutions containing 2 and 4 per cent of the acids andthickened with gum affedted the tissue less than when no thickening wasused. The adtion of acetic acid, even the glacial, is very slight; if atissue be steeped in it and then dried scarcely any alteration takes place.

* It is not improbable that part of the effedt of the organic acids on cellulose may havebeen due to an admixture of traces of some mineral acid, such as sulphuric or nitric acid,